As a communication system which is mounted on an airplane or a land mobile vehicle, a communication system in which an artificial satellite is used as a relaying station has been studied, and a microstrip antenna is supposed to be a prospective antenna which will be used therein because of having advantages such as small size and light weight.
FIG. 9 is a perspective view showing a microstrip antenna which is used in the communication system.
The microstrip antenna shown in FIG. 9 is mounted and used, for example on a body of an airplane, and includes a fairing 102 and two microstrip array panels 104 and 105. The fairing (radome) 102 in which a frame 103 is disposed is fitted on to a base 101. The two microstrip array panels 104 and 105 are mounted on this frame 103.
Each of the microstrip array panels 104 and 105 is provided with a base plate 106 made of low dielectric, a gland surface 107 formed on the reverse side of the base plate 106, and a plurality of driver elements 108 formed on the surface of the base plate 106.
And, a phase in a signal supplied to each of the driver elements 108 or in a signal received by each of the driver element 108 is shifted to a given degree by a phase shifter which is not shown in the drawing. Therefore, each area to which each microstrip array panel faces at an angle of 180.degree. is scanned in directivity, and an omni directional communication is made possible by the two microstrip array panels which are in both of the right and left sides.
However, in the microstrip antenna in which the two array panels are placed back to back, as shown in FIG. 10, in a range of a small scanning angle from an imaginable plane perpendicular to the microstrip array panel 104 or 105, a sufficient gain is obtained whereas in a range of a large scanning angle from the imaginable plane perpendicular to the microstrip array panel 104 or 105, a sufficient gain is not secured. Therefore, there is a disadvantage such that a communication in that direction becomes difficult.
Accordingly, it is an object of the present invention to provide a microstrip antenna capable of solving the disadvantage as described above as well as of securing sufficient gains in omni directions.